A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core plate and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. The core center axis is substantially coaxial with the center axis of the shroud, and the shroud is open at both ends so that water can flow up through the lower end of the shroud and out through the upper end of the shroud. The shroud, top guide, and core plate limit lateral movement of the core fuel bundles.
The shroud, due to its large size, is formed by welding a plurality of stainless steel cylindrical sections together. Specifically, respective ends of adjacent shroud sections are joined with a circumferential weld. The weld joint supports vertical and lateral loads associated with all modes of reactor operation.
The shroud welds, however, increase the susceptibility of the shroud material to a detrimental effect known as inter-granular stress corrosion cracking (IGSCC). Typically, cracking may occur in the heat affected zone of the shroud welds. Currently, volumetric inspections are performed to detect and evaluate the extent of cracking. If the cracking is determined to be significant, repairs may be performed to re-establish the integrity of the weld joint by the addition of alternate load paths.
It would be desirable to provide a shroud which has welds that are easy to inspect and, if necessary, repair. It also would be desirable to provide such a shroud which does not add significant costs to the fabrication of the shroud.